Giving one dose of steroids to babies in the womb does not have long-term detrimental effects on a child's health, a study has found.
Premature babies can suffer from lung damage
New Zealand scientists looked into concerns over the use of the steroid dexamethasone to prevent foetal respiratory distress syndrome.
But they found one course of treatment to prevent such lung damage in the foetus appears to be safe.
The study is published in the British Journal of Obstetrics and Gynaecology.
Previous research had raised concerns steroid treatment could affect a developing baby's brain and heart.
But it is the only effective treatment for preventing lung damage.
Airways in the lungs should be lined with a liquid called surfactant which ensures they do not stick together when a person breaths out.
One of the problems premature babies can have is a lack of surfactant.
Steroids given to the mother stimulate the cells in the lining of the foetus' airways that produce the liquid, enabling babies to breath normally after they are born.
Doctors in the UK have moved away from using repeated steroid treatments, but concerns remained over the potential long-term effects of one-off doses.
The New Zealand researchers, from the University of Auckland, examined the effect of one, as opposed to repeated courses of steroid treatment.
The team carried out their research on sheep.
When lambs were around 97 to 99 days gestation - the same stage of gestation as a 32-week-old human foetus - they were given a course of the steroid treatment.
They had undergone surgery while in their mother's womb to insert catheters to allow the measurement of blood pressure.
It was found that the treatment led to only a short-term increase in blood pressure, and no effect on the brain.
Dr Laura Bennet, who led the research, said: "We are currently conducting more experiments to verify these results and to make sure that even limited exposure of the foetus to steroids really does not cause problems at this most vulnerable time in life."
Dr Pat O'Brien, a consultant obstetrician and gynaecologist at University College London Hospital, said: "This is a very helpful study.
"Previous work had suggested there was no long-term harm from one-off treatments. This is an important study which reinforces that."